Display devices ("displays") for computer systems emit light from grids of tiny rectangles known as pixels. In color displays, each pixel emits light of three colors (typically, red, green, and blue), with the intensity of each color controlled by the computer system.
In cathode ray tube (CRT) color displays, each pixel consists of three phosphor dots: a red phosphor dot, a green phosphor dot, and a blue phosphor dot. Three electron beams are aimed by electromagnets at selected ones of the pixels, with all three beams simultaneously incident at each pixel (each beam incident at a different one of the dots of the pixel). The electromagnets typically cause the beams to scan the pixels sequentially in raster fashion.
Even if a computer system sends identical control signals (specifying the same combination of electron beam intensities) to different displays (or to the same display at different times), many variables will affect the actual color perceived by a viewer as the beams strike a pixel, including but not limited to the following: differences between various brands of graphics cards and CRT display hardware; variations in the circuitry controlling each of the beams of a display; the age of the phosphor dots on which the beams are incident; the ambient lighting conditions around the display; and the strength of the Earth's magnetic field and electromagnetic interference at a given time and place.
Thus, it is desirable from time to time to measure and calibrate at least two characteristics of the pixels (or representative ones of the pixels) of a display: "gamma" and "white point." The "white point" of a pixel is the pixel's perceived color when the computer causes emission of maximum values of red, blue and green light from the pixel. By commanding the computer to change the relative intensities of the maximum emitted levels of red, blue, and green, the display's "white point" can be changed. Examples of standard white points (having well-known definitions) are: 9300K (9300 degrees Kelvin); and D50 (approximately 5000 degrees Kelvin). The relative intensity of the maximum red value (100% red) to that of the maximum green or blue value at a white point of "D50" (the North American industry standard for proofing color photographs) is higher than at a white point of "9300K" (the white point to which many commercially available color monitors are factory-preset).
"Gamma" denotes the relationship between the luminance input sent to a display (from a computer system's graphics card and imaging application software) and the resulting light intensity perceived by a viewer of the display. Many variables affect the consistency of this relationship, including such variables as phosphor age and composition, graphics card and display type, and ambient lighting. Conventionally, computer systems include means for changing a display's gamma setting, to either simulate or compensate for the way other devices display or interpret the relationship between a pixel's lightness and color as it relates to the CRT emitted lightness and color. For example, a low gamma setting may be selected to compensate for the loss of detail that is inherent when displaying shadowed areas of a scanned image on a display device. Or, a high gamma setting may be selected to simulate the way a displayed image would appear if displayed on a television monitor (rather than on a conventional computer display device).
Another important aspect of controlling a display device is to control the size and geometric shape of the displayed images. Some conventional displays and computer systems include means for changing the rectangular dimensions (and edge locations) of a picture area in which images are displayed on a display screen, and for controlling "pincushion" and "barrel" side distortion and trapezoidal side distortion which cause the picture area to have a non-rectangular appearance.
Some conventional displays include mechanical controls (e.g., manually actuatable knobs or buttons) for controlling the size and/or geometric shape of the picture area in which images are displayed. Many conventional displays include mechanical controls for brightness and contrast.
Some conventional computer systems have software which displays "virtual" controls, which simulate mechanical controls, and which can be selected to control characteristics of a display such as brightness, contrast, displayed image size and shape, "gamma," and "white point." To implement such virtual controls, the system is programmed with user interface software which causes a display device to display icons (tools) resembling mechanical controls (e.g., a pair of icons having the appearance of a button labeled "+" for increasing the value of a parameter of the display, and a button labeled "-" for decreasing the parameter's value). The software causes the computer system to vary display parameters in response to user selection of various ones of the icons using a mouse or other input device. For example, each time a user operates a mouse to "click" on an icon representing a "+" button, the software may cause the system to increase incrementally the value of a display parameter corresponding to the "+button" icon. Examples of such conventional display control user interface software are the "GeoTweak.TM." product available from RasterOps Corporation, the "CONTROL TOOL" software product available from Miro (for use with "miroPROOFSCREEN" color monitors available from Miro), the "intellicolor" product available from Radius, Inc., and the "Adobe Photoshop" software product (which includes "Adobe Photoshop Gamma Control Panel" software) available from Adobe Systems Inc.
However, conventional display control hardware and software have been limited by their design simulating mechanical controls, and thus have not enabled users to control a variety of display parameters all in a convenient, intuitive manner.
Also, conventional display control hardware and software have not provided convenient means for enabling an end user to "lock in" a selected set of display parameters (so that the parameters cannot easily be changed inadvertently, or changed by an unauthorized user), and for enabling the end user to "unlock" the parameters to change them when desired. Rather, the manufacturers of conventional systems have recommended that users take the inconvenient step of placing tape over mechanical controls of a display to prevent the settings of such controls from being readily changed.
Computer hardware and software systems have also been developed which enable an end user of a computer system to calibrate parameters of the system's display. For example, the "CALIBRATION TOOL" hardware/software product available from Miro (for use with "miroPROOFSCREEN" color monitors available from Miro) includes a color sensor which can be fastened to a display screen by a suction cup, and software for calibrating the display in response to data measured by the sensor. The CALIBRATION TOOL software allows the end user to save the results of a calibration operation as monitor profile data.